Catheters are used in numerous medical procedures. In particular, catheters are used for the introduction or removal of fluids from various venous and/or arterial regions and vessels throughout the body, such as for hemodialysis. The procedure by which these catheters are introduced to the body is delicate and complex. One particularly intricate challenge to catheterization is enlarging a hole in the flesh and vessel to be catheterized while minimizing blood loss and trauma to the patient.
Generally, to insert any catheter in a blood vessel, the vessel is identified by aspiration with a long hollow needle in accordance with the Seldinger technique. When blood enters a syringe attached to the needle, indicating that the vessel has been found, a thin guide wire is then introduced, typically through the syringe needle or other introducer device, into the interior of the vessel. The introducer device is then removed, leaving the guide wire within the vessel with a proximal end portion of the guide wire projecting beyond the surface of the skin.
At this point, several options are available to the practitioner for catheter placement. The simplest option is to pass a catheter into the vessel directly over the guide wire, whereafter the guide wire is removed; a variation on this option has been adopted recently in which a stylet is inserted about the guide wire within the catheter and which extends distally from the catheter's distal tip to facilitate entry of the catheter through the vessel incision, or venotomy. Both of these techniques require that the venotomy be predilated; even with predilation it is commonly difficult to insert the catheter through the venotomy, in certain patients, especially using the guide wire only.
If, however, the catheter is of a relatively large diameter and/or not made of a stiff material, one preferable method of inserting the catheter into the vessel is through an introducer sheath. The introducer sheath is simply a large, stiff thin-walled tube, which serves as a temporary conduit for the catheter that is being placed. Prior to use of the sheath, usually a plurality of smaller-to-larger size dilators are used in sequence, placed onto and removed from the guide wire, to attain the appropriately large size for the venotomy. The sheath is positioned by placing the final dilator to be used, which has a hollow passageway along its longitudinal axis, inside of the sheath and passing both the dilator and the sheath together into the vessel over the guide wire. The dilator expands the opening in the blood vessel to allow for catheter insertion into the vessel. The guide wire and dilator are then removed, leaving the thin-walled sheath in place. The catheter is then inserted through the sheath.
In a setting where a catheter with a hub or other attachment at the end of the catheter has a feature which is larger than that of the inner diameter of the sheath, it is necessary to have a tear-away sheath that can be split away from the catheter as the sheath is being removed from the patient. In the case where a sheath does not have a small diameter or a narrow point, the dilator is often used to aid in the insertion of the sheath. The dilator has a long tubular section, the outside diameter of which is slightly smaller than the inside diameter of the sheath. The dilator also has a point tip on its distal end and a hollow center, which runs along the entire length of the dilator. The dilator is inserted into the body with the guidewire running through its center, thereby allowing the tip of the dilator to follow the guidewire to the place that is to be catheterized. On its proximal end, the dilator may have a hub. Like the hub of the sheath, this hub can also serve a number of purposes, such as providing a stable handle to aid in guiding the dilator into the vein, and as a mechanism which can mate with the sheath hub to form a locked connection.
Some dilator and sheath assemblies that include a connection between the dilator and sheath are known. U.S. Pat. No. 6,796,991 discloses a sheath and dilator assembly in which the sheath hub and the dilator hub having mating female and male threads to establish a connection therebetween, with the dilator being removable after sheath tip access to the vasculature is attained, after which the catheter is then inserted over the guide wire and into and through the sheath into the vasculature.
Dilating devices are also known for use in dilating vasculature incisions for insertion thereinto of medical tubing into the vasculature such as a catheter or an intravenous tube. One such device is disclosed in U.S. Pat. No. 2,842,133 and has two embodiments each having first and second components that together define an elongate channel through which tubing is insertable. In one version, the first and second components are affixed to respective hinged transverse spring-loaded finger pieces, and their distal portions are pivotable apart against spring bias when the finger pieces are squeezed together, to part the distal ends of the two components and dilate the vein when the pair of pieces are manually squeezed together.
It is desired to provide a dilating device that is easily manipulated and operated by the practitioner, in a single step procedure, for catheter insertion.